Increasing maxlength of media_description field

Active member

We would like to increase the number of characters in the media_description field which appears to be limited to 300 chars. We use a lot of Japanese characters (double-byte chars), further restricting the number of characters allowed. Obviously, it's not as easy as to simply switch to mediumtext or longtext.

What would be the best way to increase the maxlength of the media_description field?